The present invention relates to a typing device comprising a character-bearing disc of plastics material having a central part by which it is fixed to a selector shaft and a plurality of flexible laminae radiating from the central part, each carrying a particular character. A hammer is used to cause lamina of the selected character to strike against a sheet-bearing platen for typing. The invention particularly concerns positioning means used for angular positioning of the character relative to the typing point.
A typing arrangement of the above-mentioned kind is known, in which positioning of the character is obtained by rotation of the character-bearing disc by means of a step-wise drive and the striking is obtained by means of the hammer which selectively engages the laminae under the control of an electromagnet. With this solution typing is very fast, but the lamina is not guided, either during the approach of the hammer nor during the striking. In addition to this, angular positioning of the step-wise drive and of the character-bearing disc cannot be precise, both because of the tolerances of manufacture of the relative parts, particularly the drive rotor, and because of oscillation of the disc prior to its positioning. Therefore, both the alignment of the typing on the sheet and the neatness of the printed letters are to some extent open to improvement.
Typing arrangements are also known in which a disc of plastics material is continuously rotatable and the lamina beneath the character to be typed is caught on the fly by the hammer. The hammer has a circular rim and rectifies the position of the lamina by acting on a radial channel formed on the face of the lamina opposite that bearing the character. In this way the problem of alignment is partially solved, but to obtain sufficient robustness of the channelled laminae there is required a lamina width greater than is strictly required by the character. This involves discs of rather cumbersome diameter.